1. Field of the Invention
The present invention relates to a lighting device which is compact and efficient. It can be employed anywhere a concentrated light beam is necessary. The present invention would typically be used in a flashlight, a caution light, a light source, a reading light, a display or any of a multiplicity of lighting devices.
2. Description of Prior Art
A prior art design can be found in U.S. Pat. No. 4,698,730 issued to Sakai, et al. for a light emitting diode with its principles shown in FIG. 11 of the current application. In the FIG. 11 lighting device LP, light emitting diode (LED) element 1P is mounted at the top of a first lead frame 2P and electrically connected to a second lead 3P by a connecting wire 4P. These elements comprise a typical light emitting diode (LED) light source 5P. As described in the referenced prior art patent LED element 1P emits light forming a spatial radiation pattern that includes both forward and side emitted light. The forward emitted light generally includes light emitted within a range of divergence that includes angles of divergence between 0 and 30 degrees from the optical axis XP of the device. The side emitted light generally includes light emitted within a range of divergence that includes angles of divergence between 30 and 90 degrees from the optical axis XP of the device. In lighting device LP light source 5P is encapsulated in transparent resin 6P. Transparent resin 6P forms two optical light directing surfaces including lens 7P and peripheral reflective surface 8P both of which are symmetrical about axis XP. Both optical surfaces are surfaces of revolution about axis XP. Peripheral reflective surface 8P is a classical parabolic reflector developed about axis XP and shaped to reflect side emitted light to direct it to become parallel to axis XP. As a result of peripheral reflective surface 8P, typical side emitted light ray R1P emitted from LED element 1P intersects peripheral reflective surface 8P and is reflected such that it becomes parallel to axis XP. Planer end portion 9P is perpendicular to reflected light ray R1P and axis XP so planer end portion 9P does not refract reflected light ray R1P or change its direction. Interior wall 10P is parallel to both axis XP and reflected light ray R1P so it also does not refract or redirect light. Lens 7P refracts forward emitted light to direct it to become more parallel to axis XP. As a result of lens 7P, typical forward emitted light ray R2P emitted from LED element 1P intersects lens 7P and is refracted to emerge parallel to axis XP. Lighting device LP has an outside diameter of dimension D1 and a length of dimension D2.
In the referenced prior art design, the side emitted light is not refracted or redirected after its reflection at peripheral reflective surface 8P. Prior art contours and orients peripheral reflective surface 8P so that the reflected light becomes parallel to axis XP. The reflected light leaves the device without redirection through a "planar upper surface". The referenced prior art design functions, however, it represents an unnecessarily large and massive lighting device. The lighting device becomes large because peripheral reflective surface 8P is a parabola contoured to reflect the side light to become parallel to axis XP and also to collect the side light emitted within a wide range of angular divergence from the optical axis XP. The undesirably large size of lighting device LP can be reduced but the available methods result in an unacceptable loss in efficiency. The size of the peripheral reflective surface 8P alone can be reduced by collecting a reduced angular range of side emitted light but because less light is collected, the efficiency of the device will correspondingly be reduced. The size of the entire optical portion of the lighting device LP including the peripheral reflective surface 8P can be proportionally reduced but because LED element 1P will, if it is to maintain its light output maintain its size the ratio of peripheral reflective surface 8P size verses LED element 1P size will be reduced. A reduction in this size ratio reduces the ability of the peripheral reflective surface 8P to accurately redirect the side light resulting one again in a loss in efficiency.
Therefore, in a high efficiency embodiment the referenced prior art design is larger than desired. The large size increases manufacturing costs and due to shrinkage during molding, reduces the precision of the optical surfaces. Furthermore, the larger dimensions of the prior art design require the emitted light to pass through thick sections of transparent resin 6P before exiting the lighting device and consequently experience unacceptable attenuation due to related transmission losses. The large prior art lighting device will also not be acceptable for many uses due to the size limitation of many products.
FIG. 12 also demonstrates an additional advantage of the present invention. Looking at prior art lighting device LP it can be seen that side light emitted by LED element 1 travels a very short distance to a near point NP1 on its reflector while other light emitted by LED element 1 travels over four times that distance to a far point FP1 on the reflector before being reflected. Referring to the present invention lighting device L1 travels a short distance to near point NP2 on its reflector while other light emitted by LED element 1 travels just over two times that distance to far point FP2. The extreme difference between the near and far light paths of prior art lighting device LP makes it difficult for its optical surface to direct the light equally. The short near point NP1 is undesirable because small variations in the peripheral reflector will misdirect the light. If prior art increases the short near point distance the entire device becomes too large very quickly. In the present invention the hear point NP2 distance is at the start longer relative to prior art. Furthermore, due to its size relative to the far point distance, it can be increased without making the lighting device too large.